It is known that, when a voltage is applied between arbitrary two legs of a cockroach, since cockroaches secrete adhesive substance on the underside of tip parts of their legs, they are very sensitive to the electric shock.
The below-described experiment examined, by applying various values of voltages between two legs of cockroaches, what degree of electric shocks they have to those various voltages.
In the experimental setup shown in FIG. 1, 1a and 1b are band shaped electrodes made of aluminum plates or the likes, they are disposed in parallel to each other keeping an insulation spacing W on an insulator plate 2. Then, dc voltages are applied by a dry cell 3 between those electrodes 1a and 1b.
Hereupon, letting a cockroach 4 creeping around over the insulator plate 2, when any two legs of the cockroach 4 touch with the electrodes 1a and 1b thereacross, a dc voltage by the dry cell 3 is applied between those two legs of the cockroach 4.
Then, by varying the voltage of the dry cell 3 to various values, degrees of reactions to the electric shock at those various applied voltages were examined and the obtained results are as shown in the following Table 1.
TABLE 1 ______________________________________ kind voltage Black cockroach Brown wing cockroach ______________________________________ 4.5 V no reaction at all same to the left 6 jumping by running away by feeling shock feeling shock 9 jumping around by same to the left feeling strong shock 22.5 appearing momentary same to the above cramp 30 appearing faint and same to the above turning over ______________________________________
From the above results, it is understood that cockroaches start to feel the electric shock at about 6 volts.
And from measurements of resistances between two legs of these cockroaches, they were found to be about 2 M.OMEGA. for black cockroaches while about 1 M.OMEGA. for brown wing cockroaches.
From the above-described experiment, since cockroaches start to react at about 6 volts, in current values, it is understood that the electric shock starts at about 3 .mu.A for black cockroach and 6 .mu.A for brown wing cockroach, respectively.
From the above cockroach electric shock test, it was found that the cockroaches sensitively feel the electric shock; in the experiment described below, wherein an experimental setup of FIG. 1 is held in a vertical plane keeping the direction of the electrodes 1 and 2 laterally, when tested cockroaches were set free on an insulation plate 2 at the part below the electrodes 1 and 2, letting them creep crossing the electrodes 1 and 2 upward, it was tested, at various voltages, whether the cockroaches can pass across the electrodes 1 and 2 or not.
In Table 2, the result is shown.
TABLE 2 ______________________________________ kind voltage Black cockroach Brown wing cockroach 9 V about 50% drop 100% drop by about 50% pass electric shock 18 V about 90% drop 100% drop by about 10% pass electric shock 22.5 V 100% drop 100% drop by electric shock ______________________________________
In this manner, it is possible to let cockroaches fall down by giving them appropriate electric shocks, and therefore, by applying voltages of about 10 volts or higher for brown wing cockroach and about 20 volts or higher for black cockroach on a vertical plane, the movement of cockroaches across the electrodes can be prevented.
After giving the cockroaches experiences of electric shocks several times as described above, soon they become to stop in front of the electrodes and intend to go back in the opposite direction, and finally they never intend to come to the vicinity of the electrodes.
This is because the cockroaches gain a kind of learning effect after they experienced electric shocks several times, and they start to defend themselves when they infer something dangerous in their sights.
This is also understood from the fact that, after their experience of electric shocks, they react other dummy electrode made of the same material but having no voltages at all. Therefore, with this kind of apparatus, besides giving electric shocks, a kind of evasive effect to make cockroaches kept out from the apparatus is also be obtainable.
Hereupon, by providing the above-mentioned configuration on a wall plane part 5a around an opening part 6 for putting in and putting out things of a storing cabinet 5, invasions of a cockroach 4 into a storing space 5b can be made difficult. That is, the cockroach 4 creeping from the outside plane 5c touches across electrodes 1a, 1b on its creeping way to the storing space 5b, and thereby receiving an electric shock falls down outside the storing space 5b as indicated by an arrow mark A.
However, the cockroach 4 may not only fall down outside the storing space 5b as described above, but it may occasionally fall inside the storing space 5b as indicated by an arrow mark B, and in such a case the cockroach 4 is allowed to enter the storing space 5b. Namely, since the cockroach 4 is of light weight, by the effects of air flows or of the posture of its falling, occasionally it may happen to fall inwards the storing space 5b.